Method and apparatus for fiberizing and cellulosic product thereof

ABSTRACT

A method and apparatus for fiberizing feed stock in the form of shreds or the like to form a low density cellulosic product. The shredded feed stock is fed to a material handling rotor that functions as a centrifugal blower. The apparatus includes a housing that defines a cylindrical rotor chamber formed about a horizontal axis and a volute-shaped internal passage having at least one convolution formed around the rotor chamber. Located within the housing is a cylindrical screen with perforations that open into the rotor chamber. The centrifugal blower rotor is mounted in the rotor chamber and has a plurality of radial vanes with rakes attached to the outer ends closely spaced from the inner surface of the screen so that they continuously wipe pass the perforations to prevent clogging or blinding.

BACKGROUND OF THE INVENTION

This invention relates to the production of low density, cellulosicproducts such as fibrous thermal insulation, and especially to animproved method and apparatus for producing such products. Moreparticularly, the invention relates to a novel method and apparatus thatutilize the energy generated by producing a high velocity flow of airwith shreds of feedstock entrained therein, combined with mechanicalaction to fiberize the material with minimal damage to the fibersthemselves.

Typically, dry process comminuting the organic materials for use asthermal insulation, absorbent pads, filters, and the like is achieved byusing conventional hammer mills.

Hammer mills for performing the comminuting operation are shown in thefollowing U.S. Pat. Nos.:

    ______________________________________                                               1,777,905     2,494,107                                                       1,934,180     2,505,023                                                       2,045,582     3,143,303                                                       2,082,419     3,429,349.                                                      2,098,480                                                              ______________________________________                                    

It has been found that the use of hammer mills cannot produce afiberized mass that will optimize the physical properties of low massdensities, high thermal resistance to heat flow, high moistureabsorbence, and an acceptable aesthetic appearance.

For example, cellulose thermal insulation produced in conventionalhammer mills results in products containing less than 50 percent of themass at optimum fiber size needed to provide a low weight per cubic footand high resistance to heat flow (R value). Typically, these productscontain large (0.250 to 0.500 inch diameter) pieces of unfiberedmaterial and a large percentage of fines or dust.

In a given volume of such insulation, the following particle sizes maybe observed.

    ______________________________________                                        Coarse pieces        20 to 40%                                                Optimum fiber size   less than 50%                                            Fines or dust        10 to 30%                                                ______________________________________                                    

Hammer mill design, as is apparent from the above-listed patents,utilizes hammers or beaters that are pivotally mounted on a series ofdisks that rotate within a partial cylindrical sizing screen. Thefeedstock is typically fed into the mill via an airstream flowingperpendicular to the rotating hammers. The entire mass of feedstock isthen drawn down into a wedge-shaped space and onto the beginning of thesizing screen comprising a major pinch point and then forced through andover a typical semicylindrical screen.

Due to the extraordinary pressure exerted on the screen at the entrypinch point, heavy guage 3/16 to 1/4 inch thick, perforated metalscreens are needed to prevent breakage from fatigue. The heavy guagefurther limits the perforated open area to 30 to 40% and restricts thepossible use of smaller perforations.

As a result of the input feed method, the swing hammers will retract asthe feedstock is worked through the screen, thereby reducing the airflow due to a relatively thick mat of material, blinding the screen, andincreasing the feed residence time within the machine, resulting infines and dust. This deficiency is often mitigated by using screens withlarger perforations. This results in large unfibered pieces remaining inthe product.

Another deficiency is that the hammers are supported between disks,which, in turn, prevent complete utilization of the comminuting screensurface, adding to the blinding of the perforations. As most of thesystems are set up to be air-swept, blinding of perforations can have amajor negative effect by retarding air flow and increasing energyconsumption and product degradation.

Other types of comminuting or disintegrating apparatus have beendeveloped for producing fibrous, cellulosic product, such as thermalinsulation, and typical units are disclosed in the following U.S. Pat.Nos.:

    ______________________________________                                               1,749,954     3,986,676                                                       3,255,793     3,987,968                                                ______________________________________                                    

While these devices are capable of producing product without thepulverizing effect caused by hammer mills, they do not reduce many ofthe disadvantages outlined above.

The method and apparatus of the present invention, however, resolve manyof the problems listed above and provide other features and advantagesheretofore not obtainable.

SUMMARY OF THE INVENTION

It is among the objects of the present invention to provide a dryprocess fiberization method and apparatus for producing a fiberizedfluffy mass containing a greatly improved and uniform particle sizedistribution from fibrous organic and inorganic pieces, shreds, orfragments of isotropic feedstocks.

Another object is to produce a cellulosic thermal insulation producthaving a substantially lower mass density and improved resistance toheat flow.

A further object is to produce a fiberized mass to be used for absorbentpads, filter media, and other commercial and industrial fiber use.

Another object is to fiberize materials that will be aesthetically moreattractive to provide greater consumer appeal.

A further object is to provide a machine that is substantially moreenergy-efficient per unit of product output over prior art devices.

Another object is to provide an apparatus where the feedstock enters thefiberization zone through a plurality of axial and radial spacesresulting in a uniform distribution of pressurized and high velocityfiberization in a dilute phase environment.

A further object is to provide an apparatus which provides a positiveand consistent fiberizing action without blinding the internal sizingscreens.

Another object is to provide in such apparatus internal air/fiberseparation, thereby greatly reducing the size of downstream supportequipment needed due to the large volume of air utilized within theinvention.

These and other objects and advantages of the invention are achievedwith the unique method and apparatus of the invention whereby shreddedfeedstock entrained in an airstream flowing in a duct is fed to amaterial handling rotor that greatly increases the velocity of theflowing stream of air and utilizes the energy thus produced togetherwith mechanical action to: (1) separate the feedstock as much aspossible into individual fibers, (2) centrifugally separate the fibrousproduct from a large part of the flowing airstream, and then (3) deliverthe resulting product for further processing.

In accordance with the apparatus of the invention, a housing is providedwith spaced, parallel side walls and a curved end wall that define acylindrical rotor chamber formed about a horizontal axis perpendicularto the side walls. The housing also defines a volute-shaped internalpassage having at least one convolution formed around the rotor chamberand centered about the axis, a tangential outlet from the volute-shapedpassage, and axial inlets, preferably, one in each of the side walls, toadmit a mixture of feedstock and air to the central portion of thecentrifugal blower chamber from opposite sides.

Two air recirculation ducts are connected between a radially inwardportion of the tangential outlet and the axial inlets for recyclingseparated air from the outlet to the rotor chamber. Also, a feedstocksupply duct is provided for delivering material to the respective axialinlets designed to provide a secondary trap for metal separation.

Mounted within the housing is a cylindrical 360- degree light-gaugescreen with 50% open area and with perforations that communicate betweenthe rotor chamber and the volute-shaped passage. A centrifugal blowerrotor is mounted in the rotor chamber for rotation about the centralaxis, the rotor having a plurality of radial vanes extending betweenside plates to define therewith a plurality of radial cells. Rakersattached to the outer ends of the vanes are closely spaced from theinner surface of the screen so that they continuously wipe past theperforations to prevent clogging of blinding.

In accordance with the method of the invention, the feedstock is fed tothe central portion of a cylindrical rotor chamber, preferably fromopposite sides and in opposite axial directions. The centrifugal blowerrotor located within the rotor chamber is driven at relatively highspeed to generate a high velocity air flow and to force the feedradially outward in the rotor chamber. The rapidly flowing mixture offeedstock and air impacts against the rakers closely spaced from thecylindrical screen so that the product is subjected to the fiberizationforces of fluid, particle, and mechanical velocities and surfaces.

Then, the resulting mixture of fibers and air is centrifugally separateto form a portion of the flowing air volume free of the fibers. Theseparated air volume is returned to the rotor chamber inlet and theremaining mixture of air and fibrous product is discharged for furtherprocessing. The recycling of a large part of the system air requirmentsprevents the need to convey and use larger fans, ducts, and air/fiberseparation equipment, resulting in lower overall system energyconsumption and capital costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of the fiberization apparatus embodying theinvention;

FIG. 2 is a plan view of the apparatus of FIG. 1, with parts broken awayfor the purpose of illustration;

FIG. 3 is an end elevation of the apparatus of FIGS. 1 and 2 taken fromline 3--3 of FIG. 1;

FIG. 4 is an exploded, perspective view of the apparatus of FIGS 1, 2,and 3, with parts broken away for the purpose of illustration;

FIG. 5 is a sectional view through the apparatus taken on the line 5--5of FIG. 3, with parts broken away for the purpose of illustration;

FIG. 6 is a fragmentary, sectional view of an enlarged scale, showingthe construction of the centrifugal blower rotor used in the apparatusof the invention and taken on the line 6--6 of FIG. 5;

FIG. 7 is a fragmentary, sectional view of an enlarged scale, taken onthe line 7--7 of FIG. 6; and

FIG. 8 is a fragmentary, sectional view, taken on the line 8--8 of FIG.7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings, and initially to FIGS. 1through 4, there is shown an apparatus 10 for fiberizing preshreddedmaterial, such as paper stock, newsprint, etc. to form a low density,fibrous, product. The apparatus is placed in an overall processingsystem between a pair of inlet ducts 11 and 12 for feeding materialentrained in a stream of flowing air to the apparatus, and a dischargeduct 13 for removing the resulting fibrous product from the apparatus.

The apparatus includes as its principal components a housing assembly20, a cylindrical screen assembly 60 (FIGS. 4, 5, and 6) mounted withinthe housing assembly 20, and a rotor assembly 70 mounted within thehousing and screen assembly 60.

HOUSING ASSEMBLY

The housing assembly 20 is mounted on a frame 15 formed of structuralsteel members and including a horizontal base 16 with upright supports17 and 18. The housing 20 comprises a lower housing section 30 and anupper housing section 50 that are secured to one another to define acylindrical rotor chamber 21 therewithin formed about a central axis.The chamber has a pair of central openings 23 and 24 on opposite sidesthereof that receive the mixture of feedstock and air in opposite axialdirections.

The sections 30 and 50 also form a volute-shaped passage 25 (FIG. 5)surrounding the cylindrical rotor chamber 21 and which is generatedusing the circumference of the cylindrical rotor chamber 21 as ageneratrix. The volume-shaped passage 25 has at least one fullconvolution and in the embodiment shown has one and one-halfconvolutions between its initial point and a tangential outlet 26.

The lower section 30 comprises spaced, parallel, vertical side walls 27and 28 and a curved outer wall 29 connected between the side walls. Twopairs of brackets 31 and 32 are welded to the lower portion of thecurved end wall to provide a means for mounting the lower section to thebase 16. One end of the lower section defines the tangential outlet 26for the volute-shaped passage.

The section 30 defines a horizontal, upwardly facing surface with aperimetric flange 33. The tangential outlet 26 is coplanar with the topof the section, and also has a perimetric flange 34. A curved wall orpartition 35 is welded within the lower section to define thevolute-shaped passage.

As shown in FIG. 1, the lower section is provided with an access door 38which pivots about a hinge 39 at the lower end thereof to provide accessto the interior of the lower section 30. The door is secured, usingclamps 40. Also, three pivotable valve plates 41, 42, and 43 areprovided to permit the control of the recycled air flow within thepassage.

The upper section 50 also has a pair of spaced, parallel, vertical,semicircular side walls 51 and 52 and a curved end wall 53.

As best shown in FIG. 4, the section 50 defines a horizontal lowersurface with a perimetric flange 54 adapted to mate with the respectiveupper surface defined by the lower section 30. The flanges 33, 54provide a means for securing the two sections together in the assemblyof the housing. Also, the upper section 50 has horizontal reinforcingribs 56 and 57 welded to the side walls, and a lower section to definethe volute-shaped passage 25.

A pair of air return ducts 58 and 59 extend from the tangential outlet26 of the volute passage 25 to the respective inlets 23 and 24 that openinto the cylindrical rotor chamber 21. The end portions 58a and 59a ofthe ducts 58 and 59 are closed and have side openings that register withcentral rotor chamber openings 23 and 24, respectively. The inlet ducts11 and 12 are secured to the return ducts 58 and 59, respectively, nearthe end portions 58d and 59d to open thereinto. It will be seen that thevolute passage 25 directs the high velocity flow of the air volumeleaving the rotor chamber in a curved path that causes centrifugalseparation of fibers from a portion of the airstream. Accordingly, theair return ducts 58 and 59 are connected to a radially inward portion ofthe tangential outlet 26 so that the flow of air entering the ducts 58and 59 is essentially free of fibers which have become concentrated bycentrifugal force in the radially outward portion of the volute-shapedpassage. The portion of the airstream carrying the fibers enters theoutlet duct 13.

Preferably about 60 per cent of the air volume in the flowing stream ofair is returned, the remaining 40 per cent being discharged with thefibers.

SCREEN ASSEMBLY

The screen assembly 60, best shown in FIGS. 4, 5, and 6, comprises aperforate length 61 of relatively flexible steel sheet formed in acylindrical shape and supported within a frame comprising four annularribs 63, 64, 65, and 66 equally spaced and joined by axially extendingbraces. The cylindrical surface defined by the interior face of thescreen must be accurately dimensioned and supported, due to the closeclearance between the raker bars 99 of the rotor assembly 70 and theinner surface of the screen.

The screen frame 63, 64, 65, 66 is provided with a pair of brackets usedto mount the screen in the housing assembly 20. The interior surface ofthe screen defines a portion of the rotor chamber 21. The perforationsof the screen are typically between 10/64 inch and 14/64 inch indiameter, the hole pattern in the screen being formed according tostandard screen practices.

ROTOR ASSEMBLY

The rotor assembly 70 includes a cylindrical hub 71 mounted on a shaft72 that is journaled at its opposite ends in bearing blocks 73 and 74mounted on the tops of the respective supports 17 and 18 of the frame15. The shaft 72 has pulleys 75 and 76 secured to its opposite ends anddriven through belts 77 and 78, respectively, that are driven throughpulleys mounted on the output shafts of electric drive motors 81 and 82.The motors used are typically capable of producing about 200 to 250horsepower each. Accordingly, the maximum horsepower utilized to operatethe apparatus 10 is about 400 to 500 horsepower.

A central, radial partition plate 85 is mounted on the hub 71 midwaybetween its ends and a plurality of identical radial vane sections 86,87 are secured on opposite sides of the partition radially coextensivetherewith. The vane sections have angled, axially outer edges so thatthe radially inward portions 88, 89 of each vane enlarge as they extendradially outward up to a maximum width, whereafter each vane diminishesin width as it proceeds radially outwardly to the peripheral edge ofeach vane.

A pair of annular side walls 91, 92 are secured to the outer axial edgesof the vane section 86, 87 on both sides of the rotor assembly to definewith the respective vane sections and the center partition 85, radialchambers 90.

Raker bars 99 are adjustably secured to the outer end portions of thevanes 86, as shown in FIGS. 5, 6, and 7, by means of threaded fasteners101 passing through holes 94 in vanes 86 and radial slots 100 in theraker bars 99. The raker bars 99 are provided with spaced rectangularteeth 102, the tips thereof being carefully spaced from the screen 61between minimum and maximum limits. The minimum clearance is that atwhich the tips are immediately adjacent to the screen 61 withouttouching engagement. The maximum limit is determined functionally to bethat at which blinding of screen 61 and destruction of fibers do notoccur. If the clearance is too great, the screen 61 will blind over,thereby inhibiting passage of air and materials therethrough Fiberdestruction is observed as dust in the finished product. Typically, aclearance of 0.065 inch is satisfactory..

The raker bars 99 extend parallel to the axis of rotor 70, with theteeth 102 of circumferentially adjacent bars 99 being staggered in anaxial direction such that the spaces between teeth 102 of one bar 99 areoverlapped by the teeth 102 of the circumferentially adjacent bar 99, asotherwise illustrated in FIG. 8. By this means, the entire surface ofthe screen 61 is swept by the bars 99 as the rotor 70 rotates.

The inner diameter of the annular side walls 95 and 96 is approximatelyequal to the diameter of the inlet ducts 23, 24 in the housing 20 sothat, as will be apparent from FIG. 4, the flowing mixture of air withentrained feedstock enters the rotor assembly 70 from opposite axialdirections in the vicinity of the radially inward portions of the radialvane sections 86, 87 and then is propelled radially outward in theradial passages 90 toward the screen assembly 60.

OPERATION

In the operation of the apparatus thus described, the feedstock to befiberized is fed in a flowing stream of air through the inlet ducts 11and 12 to the end portions of the air return ducts 58 and 59, where boththe return air and the new mixture are introduced into the interior ofthe rotor chamber 21.

The rotor .Iadd.50 .Iaddend..[.is.]. .Iadd.can be .Iaddend.operated atrelatively high peripheral speeds ranging from 15,000 to 30,000.[.fpm.]. .Iadd.f.p.m. .Iaddend.(.Iadd.feet per minute ).Iaddend.,depending on the .[.feedstock.]. .Iadd.feedstock .Iaddend.being.Iadd.comminuted or .Iaddend.fiberized, and the pressure and velocitiesrequired, .[.thus generating.]. .Iadd.and can generate .Iaddend.internalair and material velocities .Iadd.through the screen,.Iaddend.rangingfrom .[.2,000.]. .Iadd.at least 1,000 .Iaddend.to 15,000 .[.fpm.]..Iadd.f.p.m .Iaddend.

The feedstock goes through no less than three rapidly changing pressureand velocity zones, thereby imparting fluid shear forces. Further, asthe air/material stream, flows coutercurrently through the rakers 99 atvelocities up to 15,000 fpm and collides with the oncoming rakers movingat 15,000 to 30,000 fpm, the feedstock is subjected to the dynamics ofimplosive forces in addition to the mechanical attrition.

When the fibers are of proper size, they are forced through the sizingscreen 61 at fluid pressures and velocities two to tenfold greater thantypically used in conventional hammer mill systems.

Accordingly, the combination of extremely high flow rates and continuousraking of the interior face of the screen 61 results in an extremelyeffective and advantageous separation of fibers without causingdisintegration such as would be caused in a hammer mill operation. Also,this action produces very little dust, as compared with hammer mill-typeprocesses.

After the fibers pass through the screen 61 with the air flow, theyenter the volute-shaped passage 25 and proceed at high velocity aroundthe passage in the direction of arrows F, subjecting them toconsiderable centrifugal force. The centrifugal force causes theentrained fibers to move to the radially outward zone of the passage 25so that the portion of the flow that is radially inward becomesessentially free of fibers. About 60 per cent of the flow (denoted bythe symbol F₁) then enters the two air return ducts 58 and 59 and isreturned to the rotor chamber 21. The remaining portion of the air flow(denoted by the symbol F₂), which contains a more concentrated volume ofthe cellulosic fibers, exits through the outlet duct 13 and proceeds onfor further processing.

As explained earlier, maintaining a proper clearance between the rakerbars 99 and the screen 61 is essential. Additionally, rotor speed, airvelocity through screen 61, and mesh size for the screen 61 must beproperly selected. It is theorized that the bulk of the fiberizationprocess is attributable to the high velocity flow of air through thescreen 61 and that the raker bars serve primarily to inhibit screenblinding and to agitate continuously the material adjacent to the screen61. By reason of the radial chambers 90 narrowing radially outwardly, avelocity increase of the air flow correspondingly occurs in the outerperipheral portions of the rotor 70. Also, a higher pressure zone occursadjacent to the leading surface of each vane 86 providing for maximumpressure differential over the screen 61 in the regions immediatelyadjacent to the raker bars 99. The air flow at the raker bars 99 passesnot only through the screen 61, fiberizing the material, but alsobetween teeth 102, aiding in the material agitation process. Typically,air flow through the screen 61 ranges between four (4) and fifteen (15)cubic feet per minute per square inch of screen.

Residence time of the material within rotor 70 should be kept to aminimum, and this is assured by the high velocity air flow. Failure tomaintain a sufficiently high air flow permits the feedstock to besubjected to repeated attacks by the raker bars 99, which ultimatelydestroys the fibers and produces dust.

It is desirable to retain the physical identity of the individual fibersin the finished product. Breaking or grinding the fibers is to beavoided, as this takes the form of undesired dust.

The apparatus and method of this invention produce a novel cellulosicproduct, using conventional paper feedstock as the raw material. Itpossesses the properties of (1) lower mass settled density, (2) higherthermal resistance to heat flow, and (3) a relatively uniformdistribution of fiber size particles. It contains minimal dust and nomore than minute quantities of unfibered particles. A satisfactoryproduct produced with this invention has settled densities that rangebetween 0.7 and 1.9 pounds per cubic foot, depending upon machineadjustment, as compared with densities of the same product produced withadvanced prior art equipment that ranges from 2.1 to 2.3 pounds percubic foot.

It has been found that the method and apparatus of the present inventionresult in a reduced energy demand for the production of low densityfibers. The energy reduction, for example, has been found in specificapplications to be between 30 per cent and 40 per cent less than thatrequired in a hammer mill-type system.

As explained previously, it is theorized that the fiberizing action isderived primarily from the air flow through the screen 61. While thepreferred form of the apparatus is as disclosed herein, it is possibleto generate the air flow requirements externally rather than internally.Use of negative high pressure air source external of the.[.screen/raker.]. .Iadd.screen-raker .Iaddend.combination,.Iadd.denoted by negative high pressure external air flow generator 11shown in FIG. 1, .Iaddend.along with suitable ducting, is considered tobe included within the broadest scope of this invention. In thisalternative form, it is not necessary to use vanes 86, but it isimportant that raker bars and the coaction thereof with the sizingscreen be preserved.

A particular product produced with this invention ranged between 1.3 and1.6 pounds per cubic foot settled density, depending on machineadjustments, as compared with densities of product produced withadvanced prior art equipment that ranged from 2.1 to 2.3 pounds percubic foot.

A comparison of test results obtained by Underwriters Laboratories usingprior art cellulosic products and a cellulosic product obtained inaccordance with the invention is shown in Table I below.

                  TABLE I                                                         ______________________________________                                        Insulation Product Comparisons.sup.1                                          Property         Prior Art.sup.2                                                                            Invention.sup.3                                 ______________________________________                                        Settled Density.sup.4                                                         (lbs. per ft..sup.3)                                                          Mean             2.5          1.5                                             Standard         .292         .5                                              Deviation        64           17                                              Number of                                                                     Samples                                                                       Range            2.0-2.8      1.45-1.55                                       Thermal Insulation                                                            (R/in.)                                                                       Mean             3.60         3.80                                            Standard         .094         --                                              Deviation        64           --                                              Number of                                                                     Samples                                                                       Range            3.4-3.75     --                                              Partial Size Distribution                                                     Coarse pieces    20 to 40 percent                                                                           <4 percent                                      Optimum fiber size                                                                             <50 percent  >93 percent                                     Fines or dust    10 to 30 percent                                                                           <6 percent                                      ______________________________________                                         .sup.1 Products contained dry flame retardants                                .sup.2 Based on listed manufacturers in the 1988 Underwriters Laboratorie     Building Material Directory                                                   .sup.3 As tested by Underwriters Laboratories                                 .sup.4 Vibrated to maximum settled density per ASTMC739-86.              

The resulting product has been capable of smoother and fasterapplication, using standard blowing equipment for insulation cellulosicthermal installation.

While the invention has been shown and described with respect to aspecific embodiment thereof, this is intended for the purpose ofillustration rather than limitation, and other variations andmodifications of the specific method and apparatus herein shown anddescribed will be apparent to those skilled in the art, all within theintended spirit and scope of the invention. Accordingly, the inventionis not to be limited in scope and effect to the specific embodimentsherein shown and described, nor in any other way that is inconsistentwith the extent to which the progress in the art has been advanced bythe invention.

What is claimed is:
 1. Apparatus for fiberizing organic material to forma low density fibrous product comprising:a housing defining;acylindrical rotor chamber having a central axis, a volume-shaped passageformed around said rotor chamber, a tangential outlet from saidvolute-shaped passage, and axial inlet means for feeding said organicmaterial into the central portion of said rotor chamber; a dischargeduct communicating with a radially outward portion of said tangentialoutlet for removing the fibrous product from the apparatus; air returnmeans communicating between a radially inward portion of said tangentialoutlet and said axial inlet means for recirculating a substantialportion of the air from said tangential outlet directly to said rotorchamber; means for delivering said organic material to said axial inletmeans; a perforate cylindrical screen mounted in said housing about saidaxis between said rotor chamber and said volute-shaped passage; acentrifugal blower rotor mounted in said rotor chamber for rotationabout said axis and having a plurality of radial vanes with rakersmounted at the outer ends thereof, said rakers being closely spaced fromthe inner surface of said screen to prevent clogging of the openings insaid screen; and drive means for turning said rotor at a speedsufficient to generate a flow velocity for said air and fibrous productthat is received in said volute chamber, that causes centrifugalconcentration of said fibrous product in the radially outward portion ofsaid volute chamber, whereby said fibrous product is concentrated in theradially outward portion of the flow at the tangential outlet fordelivery to said discharge duct and the radially inward portion of theflow that is received by said air return means at the radially inwardportion of said tangential outlet is relatively free of said fibrousproduct.
 2. Apparatus as defined in claim 1, wherein said axial inletmeans comprises two axial openings located on opposite sides of saidrotor chamber for feeding said organic material from opposite axialdirections.
 3. Apparatus as defined in claim 2, wherein said air returnmeans comprises a pair of air return ducts extending between saidradially inward portions of said
 4. Apparatus as defined in claim 3,wherein said air return ducts are of sufficient size to return about 60percent of the air flow volume from said tangential outlet to said axialinlets.
 5. Apparatus as defined in claim 1, wherein said screen hasopenings therein that comprise about 50 percent of the surface areathereof.
 6. Apparatus as defined in claim 1, wherein said openings insaid screen are between 5/32 inch and 7/32 inch in diameter. 7.Apparatus as defined in claim 1, wherein said rakers are radially spacedfrom the inner surface of said screen about 0.065 inch.
 8. Apparatus asdefined in claim 1, wherein said drive means operate said rotor atperipheral speeds from 15,000 to 30,000 fpm.
 9. Apparatus as defined inclaim 1, wherein said rakers are provided with a plurality of laterallyspaced radial teeth.
 10. Apparatus as defined in claim 9, wherein saidraker teeth on each vane are laterally staggered relative to the rakerteeth on adjacent vanes.
 11. Apparatus as defined in claim 1, whereinsaid rakers are radially adjustable on their respective vanes.
 12. Amethod for fiberizing organic material to form a low density, fibrousproduct comprising:feeding said organic material to the central portionof a cylindrical rotor chamber; driving a centrifugal rotor with radialvanes at relatively high speed in said chamber to generate a highvelocity air flow with said organic material entrained therein to forcesaid organic material radially outward in said rotor chamber atrelatively high velocity; forcing said material in said air flowradially outward through perforations in a cylindrical screensurrounding said rotor to fiberize said material; conveying said air andfiberized product exiting said screen at a relatively high flow velocitythrough a volute passage surrounded said screen and having a tangentialoutlet and thereby centrifugally separating said fiberized product froma portion of the air volume flowing through said volute chamber so thatsaid fiberized product is concentrated in the radially outward portionof the flow at said tangential outlet; conveying the flow from theradially outward portion of said tangential outlet through a dischargeduct to a collecting means; and returning the air flow from the radiallyinward portion of said tangential outlet comprising a substantialportion of the air volume therein directly to said rotor chamber.
 13. Amethod as defined in claim 12, wherein said organic material is fed intosaid rotor chamber through two axial openings located on opposite sidesof said rotor chamber.
 14. A method as defined in claim 12, wherein saidseparated portion of said air volume that is returned to said rotorrotor chamber comprises about 60 percent of the air flow through saidscreen.
 15. A method as defined in claim 12, wherein said air volumeflowing through said screen flows into and through a volute chambersurrounding said screen.
 16. A method as defined in claim 12, whereinsaid rotor is operated at peripheral speeds of about 15,000 to about30,000 fpm.
 17. A method as defined in claim 12, wherein the velocity ofsaid flow of air and feed stock generated by said rotor is from about2000 to about 15,000 fpm.
 18. A low density, fibrous product made inaccordance with the method of clain
 12. 19. A fibrous product as definedin claim 18 having a settled density of between about 0.7 and about 1.9pounds per cubic foot.
 20. A fibrous product as defined in claim 18,having a settled density of between about 1.3 and about 1.6 pounds percubic foot.
 21. A fibrous product as defined in claim 18, having an Rvalue of about 3.8.
 22. A fibrous product as defined in claim 18,wherein coarse pieces constitute less than 4 percent of the totalvolume. .Iadd.
 23. Apparatus for comminuting feed stock to form a lowdensity, fibrous product comprising:a housing defining: a cylindricalrotor chamber having a central axis extending within a central portionof said rotor chamber, a passage formed around said rotor chamber. anoutlet from said passage, and inlet means for feeding said feed stockinto the central portion of said rotor chamber; means for deliveringsaid feed stock to said inlet means entrained in a flowing fluid stream;a perforate screen mounted in said housing about said axis between saidrotor chamber and said passage; a rotor mounted in said rotor chamberfor rotation about said axis and having a plurality of radial members;means associated with an outermost end portion of at least one of saidradial members so as to be spaced closely adjacent said perforate screenfor preventing blinding of said screen as said feed stock passes throughsaid perforate screen; drive means for turning said rotor; and means forgenerating a fluid stream velocity of air and said feed stock of atleast 1000 f.p.m. through the perforations in said screen. .Iaddend..Iadd.
 24. Apparatus as defined in claim 23, wherein said means forgenerating a fluid stream velocity further includes an auxiliary flowgenerator. .Iaddend. .Iadd.25. Apparatus as defined in claim 24, whereinsaid auxiliary flow generator is located downstream of said outlet..Iaddend. .Iadd.26. Apparatus as defined in claim 23, wherein said fluidstream velocity produced through said perforations is between 1000 and15,000 f.p.m. .Iaddend. .Iadd.27. Apparatus as defined in claim 23,wherein said passage formed around said rotor is volute-shaped andwherein said outlet is tangential and located at the downstream end ofsaid volute-shaped passage. .Iaddend. .Iadd.28. Apparatus as defined inclaim 27, further comprising air return means communicating between aradially inward portion of said tangential outlet and said inlet means..Iaddend. .Iadd.29. Apparatus as defined in claim 28, wherein said airreturn duct is of sufficient size to return about 60 percent of the airflow volume from said tangential outlet to said outlet. .Iaddend..Iadd.30. Apparatus as defined in claim 23, wherein said screen hasopenings therein that comprise about 50 percent of the surface areathereof. .Iaddend. .Iadd.31. Apparatus as defined in claim 30, whereinsaid openings in said screen are between approximately 5/32 and 7/32inch in diameter. .Iaddend. .Iadd.32. Apparatus as defined in claim 23,wherein said rakers are radially spaced from the inner surface of saidscreen about 0.065 inch. .Iaddend. .Iadd.33. Apparatus as defined inclaim 23, wherein said drive means operates said rotor at peripheralspeeds from 15,000 to 30,000 f.p.m. .Iaddend. .Iadd.34. Apparatus asdefined in claim 23, wherein said rakers are provided with a pluralityof laterally spaced radial teeth. .Iaddend. .Iadd.35. Apparatus asdefined in claim 34, wherein said raker teeth on each vane are laterallystaggered relative to the raker teeth on adjacent vanes. .Iaddend..Iadd.36. Apparatus as defined in claim 23, wherein said rakers areradially adjustable on their respective radial members. .Iaddend..Iadd.37. Apparatus for fiberizing organic material to form a lowdensity fibrous product comprising;a housing defining; a cylindricalrotor chamber having a central axis extending within a central portionof said rotor chamber; a passage formed around said rotor chamber; anoutlet from said passage; axial inlet means for feeding said organicmaterial into the central portion of said rotor chamber; a dischargeduct communicating with said outlet for removing the fibrous productfrom the apparatus; means for delivering said organic material to saidaxial inlet means; a perforate cylindrical screen mounted in saidhousing about said axis between said rotor chamber and said passage; acentrifugal blower rotor mounted in said rotor chamber for rotationabout said axis and having a plurality of radially extending vanes;raker means disposed at an outermost end portion of at least one of saidvanes for agitating said feed stock as said feed stock passes throughsaid screen to prevent blinding of said screen, said raker means beingpositioned closely adjacent an inner surface of said screen; and drivemeans for turning said rotor at a speed sufficient to generate a flowvelocity for said air and fibrous product that is received in saidpassage, that causes centrifugal concentration of said fibrous productin the radially outward portion of said passage. .Iaddend. .Iadd.38.Apparatus for comminuting feed stock to form a low density fibrousproduct having a settled density of between about 0.7 and 1.9 pounds percubic foot comprising: a housing defining: a cylindrical rotor chamberhaving a central axis, a passage formed around said rotor chamber, anoutlet from said passage, and inlet means for feeding said feed stockinto the central portion of said rotor chamber; means for deliveringsaid feed stock to said inlet means entrained in a flowing fluid stream;a perforate screen mounted in said housing about said axis between saidrotor chamber and said passage; a rotor mounted in said rotor chamberfor rotation about said axis and having a plurality of radiallyextending members; raker means disposed at outermost end portions ofsaid radially extending members and positioned so as to be spacedapproximately 0.065 inch from an inner surface of said screen, saidrakers operating to agitate said feed stock as said feed stockapproaches and passes through said screen to thereby prevent blinding ofsaid screen; drive means for turning said rotor; and means includingsaid rotor for generating a fluid stream velocity of air and said feedstock of at least 1000 f.p.m. through the perforations in said screen..Iaddend. .Iadd.39. A method for fiberizing organic material to form alow density, fibrous product having a settled density of between about0.7 and about 1.9 pounds per cubic foot comprising: feeding said organicmaterial to the central portion of a cylindrical rotor chamber; drivinga centrifugal rotor with radial vanes at relatively high speed in saidchamber to generate a high velocity air flow with said organic materialentrained therein to force said organic material radially outward insaid rotor chamber at relatively high velocity; forcing said organicmaterial entrained in said air flow radially outward throughperforations in a cylindrical screen surrounding said rotor to fiberizesaid organic material into said fibrous product; conveying said air andfibrous product exiting said cylindrical screen at a relatively highflow velocity through a passage surrounding said cylindrical screen andhaving an outlet and thereby centrifugally separating said fibrousproduct from a portion of the air volume flowing through said passage sothat said fibrous product is concentrated in the radially outwardportion of the flow at said outlet; using a raker bar disposed at anoutermost end portion of at least one of said radial vanes andpositioned closely adjacent an inner surface of said screen to agitatesaid material as said material passes closely adjacent said perforationsin said cylindrical screen just prior to said material passing throughsaid perforations, to thereby prevent blinding of said screen by saidmaterial; and conveying the flow of said fiberized product from saidoutlet through a discharge duct to a collecting means. .Iaddend..Iadd.40. A method for comminuting feed stock to form a low densityproduct comprising:feeding said feed stock to a central portion of acylindrical rotor chamber; generating a high velocity fluid flow of airwith said feed stock entrained therein to force said feed stock radiallyoutward in said rotor chamber at relatively high velocity; driving arotor having radial rakers about a central axis of said rotor chamber,said rakers being closely spaced from the inner surface of a perforatecylindrical screen mounted around said rotor; forcing said resultingfluid flow radially outward through the perforations of said screen at afluid stream velocity of at least about 1000 f.p.m. through theperforations in said screen in comminute said feed stock; using saidrakers to prevent blinding of said screen by said feed stock and toagitate said feed stock closely adjacent said screen to furtherfacilitate comminuting said feed stock; and discharging the comminutedproduct. .Iaddend. .Iadd.41. A method as defined in claim 40, whereinsaid rotor further has radial vanes to which said rakers are attachedand said high velocity fluid flow is produced by the rotation of saidrotor. .Iaddend. .Iadd.42. A method as defined in claim 40, wherein saidhigh velocity fluid flow is produced in part by auxiliary glowgenerating means separate from said rotor. .Iaddend. .Iadd.43. A methodas defined in claim 41, wherein said auxiliary flow generating means islocated downstream of the location where the comminuted product isdischarged. .Iaddend. .Iadd.44. A method as defined in claim 40,including the additional step of centrifugally separating the comminutedproduct from a portion of the air volume flowing through said screen..Iaddend. .Iadd.45. A method as defined in claim 44, wherein saidseparated portion of said air volume is returned to said rotor chamber..Iaddend. .Iadd.46. A method as defined in claim 45, wherein saidseparated portion of said air volume comprises about 60% of the air flowthrough said screen. .Iaddend. .Iadd.47. A method as defined in claim44, wherein said air volume flowing through said screen flows into andthrough a volute chamber surrounding said screen. .Iaddend. .Iadd.48. Amethod as defined in claim 40, wherein said rotor is operated atperipheral speeds of about 15,000 to about 30,000 f.p.m. .Iaddend..Iadd.49. A method as defined in claim 40, wherein the velocity of saidfluid stream velocity is from about 1000 to about 15,000 f.p.m..Iaddend. .Iadd.50. A comminuted product made in accordance with themethod of claim
 40. .Iaddend. .Iadd.51. A comminuted product as definedin claim 50 having a settled density of between about 0.7 and about 1.9pounds per cubic foot. .Iaddend. .Iadd.52. A method for comminuting feedstock to form a low density product having a settled density of betweenabout 0.7 and about 1.9 pounds per cubic foot comprising:feeding saidfeed stock to the central portion of a cylindrical rotor chamber:generating a high velocity fluid flow of air with said feed stockentrained therein to force said feed stock radially outward in saidrotor chamber at relatively high velocity; driving a rotor having radialrakers about the central axis of said rotor chamber, said rakers beingradially spaced approximately 0.065 inch from the inner surface of aperforate cylindrical screen mounted around said rotor; forcing saidresulting fluid flow radially outward through the perforations of saidscreen at a fluid stream velocity of at least about 1000 f.p.m. throughthe perforations in said screen to comminute said feed stock; using saidrakers to prevent blinding of the openings in said screen by saidproduct as said product passes through said openings; and dischargingthe comminuted product to a collection means. .Iaddend. .Iadd. .Apparatus as defined in claim 23, wherein said means for preventingblinding of said screen comprises a raker adjustably secured to saidoutermost end portion of said at least one radial member. .Iaddend..Iadd.54. Apparatus as defined in claim 23, wherein said means forpreventing blinding of said screen further operates to continuouslyagitate said feed stock when said feed stock is closely adjacent saidperforate screen to thereby further help comminute said feed stock..Iaddend. .Iadd.55. A low density, fibrous comminuted product having asettled density of about 0.7 to about 1.9 pounds per cubic foot formedby:feeding feed stock into a cylindrical rotor chamber having aplurality of radially extending vanes rotating sufficiently rapidly togenerate a fluid stream having a radially outward velocity through thescreen of at least about 1000 feet per minute; causing said fluid streamhaving said feed stock entrained therein to be passed through a screenpositioned closely adjacent outermost end portions of said vanes tothereby comminute said feed stock; using a plurality of raker barsdisposed at said outermost end portions of said vanes to preventblinding of said screen and to further agitate said feed stock to aid incomminuting said feed stock; and discharging said comminuted feed stockrepresenting said product from same rotor chamber. .Iaddend. .Iadd.56. Acomminuted product as defined in claim 55 having a settled density ofbetween about 1.3 and about 1.6 pounds per cubic foot. .Iaddend..Iadd.57. A comminuted product as defined in claim 55 having an R valueof about 3.8. .Iaddend. .Iadd.58. A comminuted product as defined inclaim 55, wherein said product comprises coarse pieces and fine pieces,and wherein said coarse pieces constitute less than about 4 percent ofthe total volume of said product. .Iaddend.